Multiple accessing is a technique for identifying different users and duplexing is a technique for identifying uplink and downlink. Similarly to the multiple accessing, the uplink and downlink can be identified in frequency, time, and code domains. The duplexing is classified into frequency division duplexing (FDD), in which the uplink and downlink are identified according to frequencies, and time division duplexing (TDD) in which the uplink and downlink are identified according to times.
In the FDD, frequencies having the same magnitude are symmetrically allocated in the uplink and downlink. The FDD has been widely used due to its structure suitable for symmetric services (e.g., voice calls). In recent years, however, researches on the TDD have actively been conducted due to its structure suitable for asymmetric services (e.g., Internet services). In the FDD, since the uplink and the downlink are identified in the frequency domain, seamless data transmission can be achieved between a base station (BS) and a user equipment (EU) in the time domain for each link.
The TDD is suitable for the asymmetric services since time slots each having a different ratio can be allocated for the uplink and downlink. In addition, a channel condition is almost constant in the uplink and downlink since data is transmitted and received in the same frequency band in the uplink and downlink. Therefore, the channel condition can be immediately estimated when a signal is received. Accordingly, the TDD is suitable for an array antenna technique.
In the TDD, an entire frequency band is used for uplink or downlink, and the uplink and downlink are identified in the time domain. Thus, the frequency band is used for the uplink for a certain period of time and is used for the downlink for the remaining periods of time, thereby disabling simultaneous data transmission/reception between the BS and the UE. If the uplink and downlink are alternately allocated with the same period of time, the BS does not have to inform whether a specific time point is used for uplink transmission or downlink transmission.
In general, scheduling information includes radio resource assignment regarding a radio resource allocated for uplink or downlink transmission. However, the number of downlink subframes may differ from the number of uplink subframes in the TDD system. Further, the number of uplink subframes may be greater than the number of downlink subframes. In addition, switching patterns may be asymmetric between the downlink subframes and the uplink subframes. In this case, uplink or downlink radio resource assignment is not sufficient to indicate a specific subframe. For further accurate scheduling, there is a need for a method of transmitting new scheduling information in the TDD system.